The present invention relates to a method for transmitting data in non-connected mode by means of a mobile station comprising a step of determining the maximum data packet transmission size, known by the term MDS, standing for maximum data size in English (or MMDS, standing for Mobile MDS).
The invention relates to the field of communications made from a mobile station in the context of the GSM standard. Such a mobile station is composed of an item of mobile equipment and a smart card known as a SIM (standing for Subscriber Identity Module) card. The mobile equipment may be a telephone, a personal digital assistant (PDA, standing for Personal Digital Assistant in English) or the like.
The communications in question in the context of the present invention can be communications between two mobile stations or between a mobile station and a distant server able to communicate with such a mobile station, such as for example a communication gateway, more commonly known by the term OTA (Over The Air in English) server.
Exact knowledge of the MDS may prove to be of great importance in the context of a protocol for communication from a mobile station since the transport layers used in this type of protocol are generally not reliable. These transport layers may in fact reject excessively long messages without sending an error message or segment messages into several data packets without guaranteeing the correct reassembly thereof. In the context of such a communication from a mobile station, it is therefore important to transmit only messages with a length less than or equal to the MDS in order to avoid any risk of segmentation or rejection.
Firstly, it is necessary to give a certain number of definitions and to specify the functioning of certain communication protocols from a mobile station.
The communication protocols in particular used in a wireless communication context (non-connected mode) follow on from WAP protocols (standing for Wireless Application Protocol) which govern data transmissions between mobile stations and a distant gateway (generally referred to as a WAP gateway).
FIG. 1 describes schematically the communication within a mobile station 10 composed of an item of mobile equipment ME, a telephone in the example, and a smart card SIM. The mobile station 10 can communicate with another mobile station 10′ or with a distant server 100. The SIM card makes it possible to procure a subscriber identification and a key in order to allow on the one hand the authentication of the subscriber on the GSM network and on the other hand the decrypting or encrypting of the data received or sent. The SIM card also enables the subscriber to access data peculiar to the GSM network and information on the services accessible.
In the example in question, the communication between the SIM card and the mobile equipment ME is governed according to the BIP protocol (Bearer Independent Protocol) which is an option of the ETSI standard “GSM 11.14” describing the SIM Tool Kit (SKT) and which defines a set of commands and situations. The BIP protocol enables the SIM card to use the communication means of the mobile equipment ME whatever the communication technology used.
Communication protocols are generally organised in several superimposed layers. A conventional configuration consists of a network layer which rests on a physical and connection layer and which supports a transport layer, other layers being able to be added, such as security, transaction, session, application or other layers, according to the protocols in question.
The network layer most commonly used is configured according to the IP protocol (Internet Protocol). This IP network layer manages the interface between the physical transmission architecture and the upper layers, and essentially provides a function of routing data packets (also known as datagrams) as far as the destination, this function also being known by the term router. The IP protocol is not reliable in the event of loss, damage or duplication of data packets: namely the delivery of the datagrams is not guaranteed. It is generally for the upper layers to manage this type of situation.
The transport layer allows complete transfer of the data. There are essentially two protocols for configuring the transport layer. The TCP protocol (Transmission Control Protocol), as a connected mode protocol, guarantees the integrity and reliability of the data transmissions. The UDP (User Datagram Protocol) or WDP (WAP Datagram Protocol) on the other hand are non-connected mode protocols and are not considered to be reliable since they do not guarantee control of the data transfer. Because of their simplicity, they do however have the advantage of allowing a rapid transmission. These UDP or WDP transport protocols act as simple multiplexers/demultiplexers of data packets. These two transport protocols are very close together in their characteristics, or even identical in the case of certain types of connection (GPRS, CSD).
The MDS is a restriction in the transport layer (the UDP layer for example) on the maximum number of data octets which can be accepted in the transmission of a single data packet (a datagram). If a message includes more octets than the size of the MDS, the transport layer destroys it without transmitting it to the upper layers or segments it into a plurality of data packets which the receiver is not able to reconstitute.
Rejection of the messages must obviously be avoided. Likewise, segmentation of the messages must also be avoided as far as possible, in particular in the case where the UDP protocol is used for the transport layer. This is because segmentation often gives rise to data losses without the sending layers being advised of this.
It is therefore preferable for the SIM card to transmit only sufficiently short messages to avoid their segmentation (or rejection) by the transport layer of the host mobile equipment ME. Knowledge of the MDS then becomes important in order to use the capacities of the transport layer to the maximum possible extent without risking alienating the data transmitted. If the information to be transmitted is greater than that able to be contained in a single message, it is necessary for the SIM card to form a data block composed of several messages M.
FIG. 2 illustrates the structure of a message M. Each message M comprises a header H and information P (or payload in English). The header H is necessary for indicating the length of the message and its composition (for example a request to determine the MDS). Other information can naturally be entered in the header H according to the functionalities offered by the message protocol in question (for example its position with other messages in a block, the need for an acknowledgement, or the like). The length of the header H is minimised in order to allow a maximum amount of information transfer P. Thus an optional header can be provided in the case of additional parameters to be transmitted.
FIG. 3 illustrates the principle of segmentation of a message M by the transport layer UDP. The message M will be divided into a plurality of data packets D (datagrams) to the size of the MDS. Each packet D then comprises a header which does not make it possible, once arrived at its destination, to assemble it with the other packets in order to reconstitute the message M. This reconstitution is in fact not guaranteed by the UDP protocol of the transport layer.
Knowledge of the MDS is therefore important in the context of communications with mobile stations using the UDP protocol for configuring the transport layer of the mobile equipment.